Atomic Layer Deposition with Plasma Source

ABSTRACT

The invention relates to method including operating a plasma atomic layer deposition reactor configured to deposit material in a reaction chamber on at least one substrate by sequential self-saturating surface reactions, and allowing gas from an inactive gas source to flow into a widening radical in-feed part opening towards the reaction chamber substantially during a whole deposition cycle. The invention also relates to a corresponding apparatus.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation application of copending U.S.patent application Ser. No. 14/009,647, filed on Oct. 3, 2013, which isa national stage entry of PCT/FI2011/050303, filed on Apr. 7, 2011, thedisclosures of both applications being incorporated by reference hereinin their entireties.

FIELD OF THE INVENTION

The present invention generally relates to deposition reactors with aplasma source. More particularly, but not exclusively, the inventionrelates to such deposition reactors in which material is deposited onsurfaces by sequential self-saturating surface reactions.

BACKGROUND OF THE INVENTION

Atomic Layer Epitaxy (ALE) method was invented by Dr. Tuomo Suntola inthe early 1970's. Another generic name for the method is Atomic LayerDeposition (ALD) and it is nowadays used instead of ALE. ALD is aspecial chemical deposition method based on the sequential introductionof at least two reactive precursor species to a substrate. The substrateis located within a reaction space. The reaction space is typicallyheated. The basic growth mechanism of ALD relies on the bond strengthdifferences between chemical adsorption (chemisorption) and physicaladsorption (physisorption). ALD utilizes chemisorption and eliminatesphysisorption during the deposition process. During chemisorption astrong chemical bond is formed between atom(s) of a solid phase surfaceand a molecule that is arriving from the gas phase. Bonding byphysisorption is much weaker because only van der Waals forces areinvolved. Physisorption bonds are easily broken by thermal energy whenthe local temperature is above the condensation temperature of themolecules.

The reaction space of an ALD reactor comprises all the heated surfacesthat can be exposed alternately and sequentially to each of the ALDprecursor used for the deposition of thin films. A basic ALD depositioncycle consists of four sequential steps: pulse A, purge A, pulse B andpurge B. Pulse A typically consists of metal precursor vapor and pulse Bof non-metal precursor vapor, especially nitrogen or oxygen precursorvapor. Inactive gas, such as nitrogen or argon, and a vacuum pump areused for purging gaseous reaction by-products and the residual reactantmolecules from the reaction space during purge A and purge B. Adeposition sequence comprises at least one deposition cycle. Depositioncycles are repeated until the deposition sequence has produced a thinfilm of desired thickness.

Precursor species form through chemisorption a chemical bond to reactivesites of the heated surfaces. Conditions are typically arranged in sucha way that no more than a molecular monolayer of a solid material formson the surfaces during one precursor pulse. The growth process is thusself-terminating or saturative. For example, the first precursor caninclude ligands that remain attached to the adsorbed species andsaturate the surface, which prevents further chemisorption. Reactionspace temperature is maintained above condensation temperatures andbelow thermal decomposition temperatures of the utilized precursors suchthat the precursor molecule species chemisorb on the substrate(s)essentially intact. Essentially intact means that volatile ligands maycome off the precursor molecule when the precursor molecules specieschemisorb on the surface. The surface becomes essentially saturated withthe first type of reactive sites, i.e. adsorbed species of the firstprecursor molecules. This chemisorption step is typically followed by afirst purge step (purge A) wherein the excess first precursor andpossible reaction by-products are removed from the reaction space.Second precursor vapor is then introduced into the reaction space.Second precursor molecules typically react with the adsorbed species ofthe first precursor molecules, thereby forming the desired thin filmmaterial. This growth terminates once the entire amount of the adsorbedfirst precursor has been consumed and the surface has essentially beensaturated with the second type of reactive sites. The excess of secondprecursor vapor and possible reaction by-product vapors are then removedby a second purge step (purge B). The cycle is then repeated until thefilm has grown to a desired thickness. Deposition cycles can also bemore complex. For example, the cycles can include three or more reactantvapor pulses separated by purging steps. All these deposition cyclesform a timed deposition sequence that is controlled by a logic unit or amicroprocessor.

Thin films grown by ALD are dense, pinhole free and have uniformthickness. For example, aluminum oxide grown by thermal ALD fromtrimethylaluminum (CH₃)₃Al, also referred to as TMA, and water at250-300° C. has usually about 1% non-uniformity over the 100-200 mmdiameter wafer. Metal oxide thin films grown by ALD are suitable forgate dielectrics, electroluminescent display insulators, fill layers formagnetic read head gaps, capacitor dielectrics and passivation layers.Metal nitride thin films grown by ALD are suitable for diffusionbarriers, e.g., in dual damascene structures.

Precursors suitable for ALD processes in various ALD reactors aredisclosed, for example, in review article R. Puurunen, “Surfacechemistry of atomic layer deposition: A case study for thetrimethylaluminium/water process”, J. Appl. Phys., 97 (2005), p. 121301,which is incorporated herein by reference.

The use of radicals in ALD processes may achieve some advantages, suchas the possibility to use thermally sensitive substrates at very lowdeposition temperatures. In a plasma ALD reactor, radicals are generatedby a plasma source. The use of a plasma source, however, may causecertain requirements or specific problems for the deposition reactor.

SUMMARY

According to a first example aspect of the invention there is provided amethod comprising:

operating a plasma atomic layer deposition reactor configured to depositmaterial in a reaction chamber on at least one substrate by sequentialself-saturating surface reactions; and

allowing gas from an inactive gas source to flow into a widening radicalin-feed part opening towards the reaction chamber substantially during awhole deposition cycle.

The expression “allowing . . . to flow” may in practice mean “guiding”,“conducting” or “guiding to flow”.

In certain embodiments, the deposition reactor is a plasma enhancedatomic layer deposition reactor, a PEALD reactor. In certainembodiments, the deposition reactor comprises a plasma source on the topside of the reactor chamber. In certain embodiments, the plasma sourceis an inductively coupled plasma source. In certain embodiments, theplasma source produces radicals used as reactants in the depositionreactor. In certain embodiments, the activated species output of theplasma source consists of radicals. In these embodiments, the activatedspecies output is radicals without substantially containing ions.

In certain embodiments, the plasma atomic layer deposition reactor(plasma ALD reactor) may be used for both plasma ALD and thermal ALD.The in-feed lines for thermal ALD may be separate from the plasma ALDsource line via which radicals are guided into the reaction chamber.

A deposition process consists of one or more consecutive depositioncycles. Each deposition cycle may consist of a thermal ALD periodfollowed by a plasma ALD period or a plasma ALD period followed by athermal ALD period. Each plasma ALD period may substantially consist ofa plasma ALD pulse period (radical generation period) and a subsequentplasma ALD purge period. Similarly, each thermal ALD period maysubstantially consist of a thermal ALD pulse period and a subsequentthermal ALD purge period. In certain embodiment, each ALD cycle maycomprise more than two pulse periods (which may be followed byrespective purge periods).

In certain embodiments, the method comprises:

allowing gas from the inactive gas source to flow into the radicalin-feed part via a plasma source during a plasma precursor pulse periodof a plasma atomic layer deposition period, the gas during that pulseperiod functioning as carrier gas for generated radicals.

In certain embodiments, the method comprises:

allowing gas from the inactive gas source to flow into the radicalin-feed part via the plasma source during a purge period of a plasmaatomic layer deposition period, the gas during that purge periodfunctioning as purge and inert shield gas.

In certain embodiments, the method comprises:

allowing gas from the inactive gas source to flow into the radicalin-feed part via the plasma source both during a plasma atomic layerdeposition period and during a thermal atomic layer deposition period.

In certain embodiments, the method comprises:

allowing gas from an inactive gas source to flow into the radicalin-feed part via a route that bypasses the plasma source.

In certain embodiments, the method comprises:

allowing gas from the inactive gas source to flow into the radicalin-feed part via both a route travelling via the plasma source and viaanother route bypassing the plasma source during the plasma atomic layerdeposition period.

In certain embodiments, the method comprises:

allowing gas from the inactive gas source to flow into the radicalin-feed part only via the route bypassing the plasma source during thethermal atomic layer deposition period, and

guiding gas from the inactive gas source that flows via the plasmasource into an evacuation line during that period.

In certain embodiments, the method comprises:

guiding inert gas towards the reaction chamber via thermal atomic layerdeposition in-feed line(s) during the plasma atomic layer depositionperiod, the thermal atomic layer deposition in-feed line(s) beingseparate from plasma source line(s) via which radicals are guided intothe reaction chamber during the plasma atomic layer deposition period.

Accordingly, in certain embodiments the deposition reactor may comprisetwo routes from an inactive gas source to the in-feed part, while insome other embodiments only a singly route is implemented. In certainembodiments, the plasma source may be separated from the reactionchamber by a gate valve or a comparable closing member closing the routevia the plasma source when needed so that then the route does notcontinue via the in-feed part into the reaction chamber, but bypassesthe reaction chamber altogether.

In certain embodiments, the method comprises using a deformable in-feedpart which is deformable between a contracted shape and an extendedshape by at least one mechanical actuator.

In certain embodiments, a substrate holder carrying at least onesubstrate is mechanically coupled to the deformable in-feed part, andthe method comprises:

causing by deforming said deformable in-feed part said substrate holdercarrying at least one substrate to lift into an upper position forloading or unloading.

According to a second example aspect of the invention there is provideda plasma atomic layer apparatus, comprising:

a gas line from an inactive gas source to a widening radical in-feedpart opening towards a reaction chamber; and

a control system configured to allow gas from the inactive gas source toflow into in-feed part substantially during a whole deposition cycle,and

the plasma atomic layer deposition reactor being configured to depositmaterial in the reaction chamber on at least one substrate by sequentialself-saturating surface reactions.

In certain embodiments, the apparatus or control system is configured toallow gas from the inactive gas source to flow into the radical in-feedpart via a plasma source during a plasma precursor pulse period of aplasma atomic layer deposition period, the gas during that pulse periodfunctioning as carrier gas for generated radicals.

In certain embodiments, the apparatus or control system is configured toallow gas from the inactive gas source to flow into the radical in-feedpart via the plasma source during a purge period of a plasma atomiclayer deposition period, the gas during that purge period functioning aspurge and inert shield gas.

In certain embodiments, the apparatus or control system is configured toallow gas from the inactive gas source to flow into the radical in-feedpart via the plasma source both during a plasma atomic layer depositionperiod and during a thermal atomic layer deposition period.

In certain embodiments, the apparatus or control system is configured toallow gas from an inactive gas source to flow into the radical in-feedpart via a route that bypasses the plasma source.

In certain embodiments, the apparatus or control system is configured toallow gas from the inactive gas source to flow into the radical in-feedpart via both a route travelling via the plasma source and via anotherroute bypassing the plasma source during the plasma atomic layerdeposition period.

In certain embodiments, the apparatus or control system is configuredto:

allow gas from the inactive gas source to flow into the radical in-feedpart only via the route bypassing the plasma source during the thermalatomic layer deposition period; and

guide gas from the inactive gas source that flows via the plasma sourceinto an evacuation line during that period.

In certain embodiments, the apparatus or control system is configured toguide inert gas towards the reaction chamber via thermal atomic layerdeposition in-feed line(s) during the plasma atomic layer depositionperiod, the thermal atomic layer deposition in-feed line(s) beingseparate from plasma source line(s) via which radicals are guided intothe reaction chamber during the plasma atomic layer deposition period.

In certain embodiments, said in-feed part defining or forming theexpansion space is variable in its dimensions or its shape or size. Incertain embodiments, said lifting mechanism is configured to change thedimensions of said in-feed part.

In certain embodiments, said in-feed part is a part via which radicalsenter the reaction chamber. In certain embodiments, said in-feed parthas a contracted shape and an extended shape, the transition betweenthese shapes being operated by a lifting mechanism (an elevator orsimilar). The elevator may be configured to push or pull said in-feedpart from said extended shape to said contracted shape allowing saidloading of said at least one substrate when said in-feed part is in itscontracted shape. In certain embodiments, said in-feed part isconfigured to deform vertically.

In certain embodiments, said in-feed part comprises a set of nestedsub-parts or ring-like members movable to fit within each other. Thesub-parts may be hollow from inside. The number of nested sub-parts maybe two or more to form a telescopic structure. The form of the nestedsub-parts may be a truncated cone. In an embodiment, where said in-feedpart practically consists of two or more sub-parts, at least thesub-part that is closest to the reaction space may be a truncated cone.In certain embodiments, said in-feed part consists of two nestedsub-parts.

In certain embodiments, the in-feed part is deformable, and theapparatus comprises at least one mechanical actuator to deform thein-feed part between a contracted shape and an extended shape.

In certain embodiments, a substrate holder carrying at least onesubstrate is mechanically coupled to the deformable in-feed part, andwherein deforming said deformable in-feed part causes said substrateholder carrying at least one substrate to lift into an upper positionfor loading or unloading.

According to a third example aspect of the invention there is provided aplasma atomic layer apparatus, comprising:

means for operating a plasma atomic layer deposition reactor configuredto deposit material in a reaction chamber on at least one substrate bysequential self-saturating surface reactions; and

means for allowing gas from an inactive gas source to flow into awidening radical in-feed part opening towards the reaction chambersubstantially during a whole deposition cycle.

Different non-binding example aspects and embodiments of the presentinvention have been illustrated in the foregoing. The above embodimentsare used merely to explain selected aspects or steps that may beutilized in implementations of the present invention. Some embodimentsmay be presented only with reference to certain example aspects of theinvention. It should be appreciated that corresponding embodiments mayapply to other example aspects as well. Any appropriate combinations ofthe embodiments may be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 shows a general framework of a deposition reactor in accordancewith an example embodiment;

FIG. 2 shows certain details of the deposition reactor in accordancewith an example embodiment;

FIG. 3 shows a reaction chamber and certain related parts of thedeposition reactor in accordance with an example embodiment;

FIG. 4 shows process instrumentation of the deposition reactor inaccordance with an example embodiment;

FIG. 5 shows an example of a timing diagram in the example embodiment ofFIG. 4;

FIG. 6 shows process instrumentation of a deposition reactor inaccordance with another example embodiment;

FIG. 7 shows an example of a timing diagram in the example embodiment ofFIG. 6; and

FIG. 8 shows a rough block diagram of a deposition reactor controlsystem in accordance with an example embodiment.

DETAILED DESCRIPTION

In the following description, Atomic Layer Deposition (ALD) technologyis used as an example. The purpose, however, is not to strictly limit tothat technology but it has to be recognized that certain embodiments maybe applicable also in methods and apparatus utilizing other comparableatomic-scale deposition technologies.

The basics of an ALD growth mechanism are known to a skilled person.Details of ALD methods have also been described in the introductoryportion of this patent application. These details are not repeated herebut a reference is made to the introductory portion with that respect.

FIG. 1 shows a deposition reactor (a plasma ALD reactor or similar) in aside view. The deposition reactor comprises a reaction chamber (notshown in FIG. 1) below a substrate transfer chamber inside an ALDreactor module 130. Source gas flows via a carrier and purge gas line101 into a plasma source 110 on the top side of the reaction chamber.Radicals generated by the plasma source 110 from the source gas flow viaa reaction chamber in-feed line or plasma source line 102 towards thereaction chamber. In between the plasma source 110 and the reactionchamber there is the substrate transfer chamber 120. At least onesubstrate is loaded into the reaction chamber via the transfer chamber120. The substrate transfer chamber 120 comprises an interface for aload lock or similar for loading said at least one substrate. In anexample embodiment, the interface may be a load lock flange 122, orsimilar, to which a load lock having a gate valve can be attached. In anexample embodiment, loading of the at least one substrate into thetransfer chamber may be an automated procedure. Alternatively, the atleast one substrate may be loaded manually. A larger hatch 123integrated to the transfer chamber is particularly suitable for manualloading and unloading in the room pressure.

The plasma source line 102 from the plasma source may be closed prior tothe transfer chamber 120 by a closing member or valve 115, such as agate valve or similar (hereinafter referred to the gate valve 115),attached to the plasma source line 102. When the valve 115 is open,radicals generated by the plasma source 110 from the source gas flow viathe plasma source line 102 towards the reaction chamber. The radicalsflow through the transfer chamber upper flange 121 into an expansionspace (not shown in FIG. 1) that widens towards the reaction chamber.This, and other additional details, is shown in more detail in FIG. 2.In an embodiment as shown in more detail in FIG. 6 and relateddescription, the closing member or valve 115 may be omitted from theconstruction and there is a protective inert gas (such as argon) flowfrom the source gas line 101 through the plasma generator 110 towardsthe reaction space (331, FIG. 3) during the deposition process.

The expansion space is defined or formed by an in-feed part or anassembly comprising a set of nested sub-parts or ring-like members whichare movable to fit within each other. In the embodiment shown in FIG. 2,the number of sub-parts is two. The sub-parts 241 and 242 form atelescopic structure. In the example embodiment shown in FIG. 2 theupper sub-part 241 is attached to the transfer chamber upper flange 121.The flange 121 may also be denoted as a vacuum chamber flange, since avacuum or almost a vacuum can typically be generated into the portion ofthe transfer chamber that surrounds the in-feed part. In the exampleembodiment shown in FIG. 2 the lower sub-part 242 is attached to anexpansion space flange 224 which, during deposition, is substantiallyleak-tightly fitted against a reaction chamber flange 234 preventing gasleaks between the reaction space (331, FIG. 3) and the gas spacesurrounding the reaction chamber (335, FIG. 3).

In the embodiment shown in FIG. 2, a retractable shaft of an elevator250 is attached to the expansion space flange 224, or directly to thein-feed part. The body of the elevator 250 may also be attached to thetransfer chamber upper flange 121 or to another suitable counterpart inthe deposition reactor. The elevator 250 may be for example an elevatorwhich operates by means of a rigid retractable shaft at least partiallycovered with bellows 251 or similar. In an embodiment, this arrangementforms a leak-tight vertically flexible cover between a pneumatic or alinear actuator and the expansion space flange 224 or the in-feed part.In an embodiment, a linear feedthrough for moving the in-feed part andexpansion space flange together with the substrate holder in vacuum andcontrolled from atmosphere side is used.

The deposition reactor shown in FIG. 2 has an optional evacuation line207 in fluid communication with the plasma source line 102. Theevacuation line 207 is joined to the plasma source line 102 on theportion of the plasma source line 102 between the plasma source 110 andthe gate valve 115.

Further, the deposition reactor shown in FIG. 2 has an optional shieldgas line 204 in fluid communication with the plasma source line 102.Inactive shield gas flowing in the shield gas line prevents particle orgas flow in the upstream direction. The shield gas line 204 is joined tothe plasma source line 102 on the portion of the plasma source line 102after the gate valve 115, in an embodiment immediately next to the gatevalve 115 in the downstream direction.

In an alternative embodiment, the expansion space flange 224 is notseparate from the in-feed part but forms part of the in-feed part thusforming a bottom part of the in-feed part. The bottom part in thatembodiment functions as a rim seal against the reaction chamber. On theother hand, it functions as a fixing point for the elevator 250(elevator shaft).

In a reaction space 331 of reaction chamber 335, as shown by FIG. 3, atleast one horizontally placed substrate 360 is supported by or lies on asubstrate holder 361. In an embodiment, the substrate holder comprisestwo separate sections with an open gap wide enough for allowing freemovement of a substrate fork between the sections. The substrate holder361 is attached to the expansion space flange 224 by holder supports362. In an example embodiment, the substrate holder 361 is configured tomove together with the expansion space flange 224. In an embodiment, thebottom end of the elevator bellows 251 is leak-tightly coupled up withthe shaft. Pulling the shaft within the elevator bellows 251 with theactuator contracts the elevator bellows 251, and the at least onesubstrate 360 or the substrate holder 361 can be pulled up for loadingor unloading while keeping the substrate handling area and itssurroundings in vacuum. The in-feed part comprising the sub-parts 241and 242 contracts vertically when the sub-part 242 slides onto thesmaller sub-part 241 leaving a space for loading and unloading via thetransfer chamber 120 (FIG. 1). There can be more than one elevator, suchas two elevators. The elevator bellows 351 of a second elevator has beenshown in FIG. 3 with dotted lines.

In an embodiment, the substrate holder 361 is detachably attachable tothe expansion space flange 224. In that way the substrate holder 361together with the at least one substrate 360 can be loaded or unloadedwhen pulled up. Similarly, a batch of substrates vertically placed in asubstrate holder can be loaded into and unloaded from the depositionreactor.

Deposition of material on the at least one substrate 360 occurs byalternating sequential self-saturating surface reactions in the reactionspace 331 of the reaction chamber 335. Alternately, radicals from theplasma source 110 (FIGS. 1 and 2) and other precursor vapor flow to thereaction space 331 of the reaction chamber 335. Radicals from the plasmasource 110 flow as a top to bottom flow 301 via the expansion space tothe reaction space 331. The other precursor vapor flow either viain-feed line 371 via an example tube fitting 381 and channel 373 withinthe reaction chamber flange 234 or via in-feed line 372 an example tubefitting 382 and channel 374 within the reaction chamber flange 234. In atypical reactor construction the number of in-feed lines is for example4 or 6. Alternatively, the other precursor may also flow into thereaction chamber 335 via the plasma source line 102 with the plasmageneration shut off. Exhaust gases are removed via an exhaust guide onthe bottom to an exhaust line as indicated with the flow direction arrow305.

In an embodiment, the gas space between the plasma generator (plasmasource 110) and the substrate holder 361 substantially consists of anopen gas space so that the majority of radicals generated by the plasmagenerator is capable of arriving essentially intact to the substrate 360without hitting any surfaces before the substrate.

FIG. 4 shows process instrumentation of the deposition reactor inaccordance with an example embodiment. An inert gas flow from an inert(or inactive) gas source is divided into a carrier and purge gas flowthat flows via the carrier and purge gas line 101 and a shield gas flowthat flows via the shield gas line 204. In an embodiment, argon orhelium, or similar, is used as the inert gas. The carrier and purge gasline 101 can be opened and closed by a carrier and purge valve 410.During operation, the default position of the valve 410 is ‘open’. Theshield gas line 204 can be opened and closed by a shield gas valve 416.During operation, the default position of the valve 416 is ‘open’. Theflow rate in the carrier and purge gas line 101 is controlled by a massflow controller (MFC) 431, and the flow rate in the shield gas line 204is controlled by a mass flow controller 432. The shield gas line 204joins to the plasma source line 102 downstream the gate valve 115.During operation, the default position of the gate valve is ‘open’. Thecombined flow flows via the plasma source line 102 and enters thereaction chamber 335 via the expansion space 425. A vacuum pump 438 isused for purging exhaust gases from the reaction space 331 into theexhaust line. The pressure transducer PT is used for verifying that theplasma source line pressure is in a suitable range for operating theremote plasma generator.

Downstream the carrier and purge valve 410 before entering the plasmasource 110, the carrier and purge gas flows through plasma sourceprecursor pulsing valves 411-414. In an embodiment, the valves arethree-way valves. The carrier and purge gas flows into a first input ofa pulsing valve and outputs via an output. In this context a precursorthat can flow via a pulsing valve 411-414 into the carrier and purge gasline 101 and can subsequently be used to generate radicals in the plasmasource 110 is denoted as plasma source precursor. The desired plasmasource precursor, depending on the applied deposition cycle, is guidedvia an MFM (Mass Flow Meter) and through a capillary or a needle valveinto a second input of a corresponding pulsing valve. During operation,the default position of valves 411-414 is that the first input andoutput are ‘open’, the second input is ‘closed’ and will be opened onlyduring plasma precursor pulse periods of a selected plasma sourceprecursor.

In the embodiment shown in FIG. 4, nitrogen gas, hydrogen gas, ammoniagas and oxygen gas serve as examples of plasma source precursors. Themass flow meter MFM 441 measures the flow rate of nitrogen gas from anitrogen gas source through a capillary or needle valve 451 to thenitrogen pulsing valve 411. Similarly, the MFM 442 measures the flowrate of hydrogen gas from a hydrogen gas source through a capillary orneedle valve 452 to the hydrogen pulsing valve 412, the MFM 443 measuresthe flow rate of ammonia gas from an ammonia gas source through acapillary or needle valve 453 to the ammonia pulsing valve 413, and theMFM 444 measures the flow rate of oxygen gas from an oxygen gas sourcethrough a capillary or needle valve 454 to the oxygen pulsing valve 414.MFMs 441-444 are used for verifying that the mass flow rate of theplasma source precursor settles to a desired value controlled with thepressure of the plasma source precursor to the upstream of the capillaryor needle valve 451-454 and with the orifice size of the capillary orwith the adjustment of needle valve 451-454. When the second input of apulsing valve is open, the corresponding plasma source precursor ismixed with the carrier gas flow and flows further towards the plasmasource 110 for radical generation.

The evacuation line 207 joined to the plasma source line 101 downstreamof the plasma source 110 and upstream of the gate valve 115 is not usedduring normal operation. Accordingly, the default position of anevacuation valve 417 (by which the evacuation line 207 can be opened andclosed) is ‘closed’.

In FIG. 4 there are also shown the other in-feed lines 371 and 372visible in FIG. 3 via which other precursor vapor may flow into thereaction chamber 335 during, for example, a thermal ALD period.

FIG. 5 shows the operation of the deposition reactor of FIG. 4 by meansof a timing diagram in accordance with an example embodiment. Thedeposition process is basically formed by repeated deposition cycles. Attime instant t₁, the gate valve 115 of the plasma source line 102 isopened. The gate valve 115 remains opened during the whole depositionprocess. At time instant t₂, the isolation valve (carrier and purgevalve 410) of the carrier and purge gas line 101 is opened. The MFC 431of the carrier and purge gas line 101 is set to a processing value,e.g., 50 sccm. At time instant t₃, the MFC 432 of the shield gas line204 is set from a high value to a low value, e.g., 20 sccm. The timebetween t₃ and t₄ can be used for purging the reaction chamber 335. Attime instant t₄, the pulsing valve of a (non-metal) plasma sourceprecursor is opened. In the example shown in FIG. 5, hydrogen gas isused as the plasma source precursor, so at time instant t₄ it is thepulsing valve 412 that is opened. At time instant t₅, the power of theplasma generator (plasma source 110) is increased to the radicalgeneration level, e.g., 2000 W. In an embodiment, the power hereinmentioned is radio frequency (RF) power. Radicals are generated duringthe time between t₅ and t₆. In other words, between time instants t₅ andt₆ a plasma ALD phase is carried out. At time instant t₆, the power ofthe plasma generator (plasma source 110) is lowered to a level whereradicals are not generated, e.g., to a power that is less than 100 W. Attime instant t₇, the pulsing valve (here: valve 412) of the plasmasource precursor is closed. At time instant t₈, the MFC 432 of theshield gas line 204 is set from a low value to a high value. The timebetween t₇ and t₉ can be used for purging the reactor chamber 335. Attime instant t₉, second precursor vapor is guided into the reactionchamber 335. In the present embodiment, the second precursor is a metalprecursor. Between t₉ and t₁₀ the second precursor pulse phase iscarried out. The time between t₉ and t₁₀ may consist of the secondprecursor pulse and the third purge period for removing surplus secondprecursor molecules and reaction byproducts from the reaction space 331while the mass flow rate of the shield gas through the shield gas line204 is at the high value for preventing the backstreaming of reactivemolecules towards the gate valve 115 and the remote plasma generator110. This can be carried out as the as-such known conventional thermalALD method. The deposition cycle formed by the purge period between t₃and t₄, the plasma ALD phase between t₅ and t₆, the second purge periodbetween t₇ and t₉, and the thermal ALD phase between t₉ and t₁₀ isrepeated until a desired thickness of material has grown onto the atleast one substrate in the reaction chamber 335. In the end, at timeinstant t₁₁, the carrier and purge valve 410 is closed, and the MFC 431of the carrier and purge gas line 101 is set to a zero value. Finally,the gate valve 115 is closed at time instant t₁₂.

An alternative embodiment concerns, for example, situations in which fora certain reason the plasma source line 102 is desired to be closed bythe gate valve 115 during a deposition process. This can occur, forexample, during the thermal ALD phase, or if the reactor is desired tocarry out a deposition process with thermal ALD phases only. In theseembodiments, the route via the pulsing valves 411-414 and the plasmasource 110 to the reaction space 331 is closed. Since a constantpressure should preferably be maintained in the plasma source 110, theevacuation line valve 417 is opened and a gas flow through the plasmasource 110 is guided via the evacuation line 207 directly to the exhaustline to maintain a constant pressure. Shield gas flowing from the shieldgas line 204 forms a shielding buffer preventing particle and gas flowfrom rising from the direction of the reaction chamber 335 into thedirection of the gate valve 115.

FIG. 6 shows process instrumentation of the deposition reactor inaccordance with another example embodiment. The embodiment shown in FIG.6 otherwise corresponds to the embodiment shown in FIG. 4 except that itdoes not contain the gate valve 115, the related evacuation line 207,the shield gas line 204 and the carrier and purge valve 410.

In certain embodiments, oxygen radicals generated from oxygen gas areused for growing metal oxides, such as oxides of group 3 metals (e.g.yttrium oxide), oxides of group 4 metals (e.g. hafnium dioxide), oxidesof group 5 metals (e.g. tantalum pentoxide) and oxides of group 13metals (e.g. aluminum oxide). Ammonia radicals generated from ammoniagas and nitrogen radicals generated from nitrogen gas are used forgrowing metal nitrides, such as nitrides of group 4 metals (e.g.titanium nitride), nitrides of group 5 metals (e.g. tantalum nitride andsuperconducting niobium nitride) and nitrides of group 14 elements (e.g.silicon nitride). Hydrogen radicals generated from hydrogen gas are usedas a reducing agent for growing elemental thin films, such as group 4metals (e.g. titanium), group 5 metals (e.g. tantalum), group 6 metals(e.g. tungsten) and group 11 metals (e.g. silver). Volatile hydrocarbonsare utilized for generating hydrocarbon radicals for growing metalcarbides, such as carbides of group 4 metals (e.g. titanium carbide).

FIG. 7 shows the operation of the deposition reactor of FIG. 6 by meansof a timing diagram in accordance with an example embodiment. At timeinstant t_(A) the MFC 431 of the carrier and purge gas line 101 is setto a processing value, preferably in the range of 10-200 sccm, morepreferably in the range of 20-100 sccm, e.g., 50 sccm. The time betweent_(B) and t_(C) is used for pulsing metal precursor vapor, e.g.trimethylaluminum (TMA), in thermal ALD mode to the reaction space 331heated to a temperature selected from a range of approximately 50-500°C., e.g. 200° C. in case of TMA used as a metal precursor. The timebetween t_(C) and t_(D) is used for purging the reaction space 331 withinert gas that consists of argon or helium gas from the plasma sourceline 102 and nitrogen gas from the in-feed lines 371, 372. At timeinstant t_(D), the pulsing valve of a (non-metal) plasma sourceprecursor is opened. Oxygen gas is selected from the available plasmasource gases in FIG. 6, so at time instant t_(D) it is the pulsing valve414 that is opened. At time instant t_(E), the power of the plasmagenerator (plasma source 110) is increased to the radical generationlevel, to the RF power selected from a range of 100-3000 W, e.g., 2000 Win case of oxygen radical generation. Radicals are generated during thetime between t_(E) and t_(F). In other words, between time instantst_(E) and t_(F) a plasma ALD phase is carried out. At time instantt_(F), the power of the plasma generator (plasma source 110) is loweredto a level where radicals are not generated, preferably to a power thatis less than 100 W, e.g. 0 W. At time instant t_(G), the pulsing valve(here: oxygen gas valve 414) of the plasma source precursor is closed.The time between t_(G) and t_(H) is used for purging the system withinert gas. The deposition cycle from the time instant t_(B) to the timeinstant t_(H) consisting of the metal precursor pulse, purge, radicalprecursor pulse and purge is repeated until a thin film of desiredthickness is grown on the substrate 360.

It is to be noted that several variants of the embodiments presentedherein may be implemented. In a construction shown in FIG. 4 thedeposition cycle may be implemented in the order shown in FIG. 5, or forexample, in the order shown in FIG. 7.

In certain embodiments, gas is guided to flow from the inactive gassource into the radical in-feed part (or expansion space 425) via theplasma generator (plasma source 110) during the plasma precursor pulseperiod of the plasma ALD period, the gas during that pulse periodfunctioning as carrier gas for generated radicals, and in certainembodiments, gas is guided to flow from the inactive gas source into theexpansion space 425 via the plasma generator during the purge period ofthe plasma ALD period, the gas during that purge period functioning asinert or purge gas. In certain embodiments, gas is guided in this wayduring both of these periods. During both of these periods, gas from theinactive gas source is additionally guided in certain embodiments intothe expansion space 425 via the shield gas line 204. During, forexample, a thermal ALD period, gas from the inactive gas source isguided in certain embodiments into the expansion space 425 via bothroutes, or via the shield gas line 204 only (in the event, the routefrom the plasma generator to the expansion space 425 is, for example,closed). Also, whenever the route from the plasma generator to theexpansion space 425 is otherwise closed, gas from the inactive gassource is guided in certain embodiments during these periods into theexpansion space 425 via the shield gas line 204 causing a continuousinert gas flow into the expansion space 425 and preventing thebackstreaming effect. If the route from the plasma generator to theexpansion space 425 is closed, gas from the inactive gas source thatflows via the plasma generator is guided in certain embodiments into anevacuation line during that period so as to maintain a constant pressurein the plasma generator.

The following experimental example further demonstrates the operation ofselected example embodiments.

Example 1

A 100-mm silicon wafer was loaded to the reaction chamber 335 with thedual elevator shown in FIG. 3. The instrumentation of the depositionreactor according to FIG. 6 and the timing diagram of FIG. 7 were usedfor growing aluminum oxide Al₂O₃ from trimethyl aluminum TMA and waterH₂O on the silicon wafer at 200° C. The flow rate of argon gas was 30sccm through the carrier and purge gas line 101. The TMA pulse lengthwas 0.1 s followed by the 6 s purge. Oxygen gas pulsing valve 414 wasopened and 50 sccm of oxygen gas was flowing through the pulsing valve414 to the remote plasma generator 110. The RF power was increased from0 W to 2500 W to switch on the plasma and kept at the 2500 W level for 6s. After that the RF power was lowered from 2500 W to 0 W to switch offthe plasma. Next the oxygen gas valve was closed and the system waspurged with inert gas for 10 s. The deposition cycle was repeated untila 36-nm Al₂O₃ thin film was grown. As a result, the 1-sigmanon-uniformity of the thin film thickness measured with an ellipsometerfrom 49 points was only 1.3%.

In an example embodiment, the deposition reactor described herein is acomputer-controlled system. A computer program stored into a memory ofthe system comprises instructions, which upon execution by at least oneprocessor of the system cause the deposition reactor to operate asinstructed. The instructions may be in the form of computer-readableprogram code. FIG. 8 shows a rough block diagram of a deposition reactorcontrol system 800. In a basic system setup process parameters areprogrammed with the aid of software and instructions are executed with ahuman machine interface (HMI) terminal 806 and downloaded via Ethernetbus 804 to a control box 802. In an embodiment, the control box 802comprises a general purpose programmable logic control (PLC) unit. Thecontrol box 802 comprises at least one microprocessor for executingcontrol box software comprising program code stored in a memory, dynamicand static memories, I/O modules, A/D and D/A converters and powerrelays. The control box 802 sends electrical power to pneumaticcontrollers of the valves of the deposition reactor, and has two-waycommunication with mass flow controllers, and controls the operation ofthe plasma source and radical generation and the elevator, as well asotherwise controls the operation of the deposition reactor. The controlbox 802 may measure and relay probe readings from the deposition reactorto the HMI terminal 806. A dotted line 816 indicates an interface linebetween the deposition reactor parts and the control box 802.

The foregoing description has provided by way of non-limiting examplesof particular implementations and embodiments of the invention a fulland informative description of the best mode presently contemplated bythe inventors for carrying out the invention. It is however clear to aperson skilled in the art that the invention is not restricted todetails of the embodiments presented above, but that it can beimplemented in other embodiments using equivalent means withoutdeviating from the characteristics of the invention.

Furthermore, some of the features of the above-disclosed embodiments ofthis invention may be used to advantage without the corresponding use ofother features. As such, the foregoing description should be consideredas merely illustrative of the principles of the present invention, andnot in limitation thereof. Hence, the scope of the invention is onlyrestricted by the appended patent claims.

1. A method comprising: operating a plasma atomic layer depositionreactor configured to deposit material in a reaction chamber on at leastone substrate by sequential self-saturating surface reactions; andallowing gas from an inactive gas source to flow into a widening radicalin-feed part opening towards the reaction chamber substantially during awhole deposition cycle.
 2. The method of claim 1, comprising: allowinggas from the inactive gas source to flow into the radical in-feed partvia a plasma source during a plasma precursor pulse period of a plasmaatomic layer deposition period, the gas during that pulse periodfunctioning as carrier gas for generated radicals.
 3. The method ofclaim 1, comprising: allowing gas from the inactive gas source to flowinto the radical in-feed part via the plasma source during a purgeperiod of a plasma atomic layer deposition period, the gas during thatpurge period functioning as purge and inert shield gas.
 4. The method ofclaim 1, comprising: allowing gas from the inactive gas source to flowinto the radical in-feed part via the plasma source both during a plasmaatomic layer deposition period and during a thermal atomic layerdeposition period.
 5. The method of claim 1, comprising: allowing gasfrom an inactive gas source to flow into the radical in-feed part via aroute that bypasses the plasma source.
 6. The method of claim 1,comprising: allowing gas from the inactive gas source to flow into theradical in-feed part via both a route travelling via the plasma sourceand via another route bypassing the plasma source during the plasmaatomic layer deposition period.
 7. The method of claim 1, comprising:allowing gas from the inactive gas source to flow into the radicalin-feed part only via the route bypassing the plasma source during thethermal atomic layer deposition period, and guiding gas from theinactive gas source that flows via the plasma source into an evacuationline during that period.
 8. The method of claim 1, comprising: guidinginert gas towards the reaction chamber via thermal atomic layerdeposition in-feed line(s) during the plasma atomic layer depositionperiod, the thermal atomic layer deposition in-feed line(s) beingseparate from plasma source line(s) via which radicals are guided intothe reaction chamber during the plasma atomic layer deposition period.9. The method of claim 1, comprising: using a deformable in-feed partwhich is deformable between a contracted shape and an extended shape byat least one mechanical actuator.
 10. The method of claim 9, wherein asubstrate holder carrying at least one substrate is mechanically coupledto the deformable in-feed part, the method comprising: causing bydeforming said deformable in-feed part said substrate holder carrying atleast one substrate to lift into an upper position for loading orunloading.
 11. A plasma atomic layer apparatus, comprising: a gas linefrom an inactive gas source to a widening radical in-feed part openingtowards a reaction chamber; and a control system configured to allow gasfrom the inactive gas source to flow into in-feed part substantiallyduring a whole deposition cycle, and the plasma atomic layer depositionreactor being configured to deposit material in the reaction chamber onat least one substrate by sequential self-saturating surface reactions.12. The apparatus of claim 11, wherein the control system is configuredto allow gas from the inactive gas source to flow into the radicalin-feed part via a plasma source during a plasma precursor pulse periodof a plasma atomic layer deposition period, the gas during that pulseperiod functioning as carrier gas for generated radicals.
 13. Theapparatus of claim 11, wherein the control system is configured to allowgas from the inactive gas source to flow into the radical in-feed partvia the plasma source during a purge period of a plasma atomic layerdeposition period, the gas during that purge period functioning as purgeand inert shield gas.
 14. The apparatus of claim 11, wherein the controlsystem is configured to allow gas from the inactive gas source to flowinto the radical in-feed part via the plasma source both during a plasmaatomic layer deposition period and during a thermal atomic layerdeposition period.
 15. The apparatus of claim 11, wherein the controlsystem is configured to allow gas from an inactive gas source to flowinto the radical in-feed part via a route that bypasses the plasmasource.
 16. The apparatus of claim 11, wherein the control system isconfigured to allow gas from the inactive gas source to flow into theradical in-feed part via both a route travelling via the plasma sourceand via another route bypassing the plasma source during the plasmaatomic layer deposition period.
 17. The apparatus of claim 11, whereinthe control system is configured to: allow gas from the inactive gassource to flow into the radical in-feed part only via the routebypassing the plasma source during the thermal atomic layer depositionperiod; and guide gas from the inactive gas source that flows via theplasma source into an evacuation line during that period.
 18. Theapparatus of claim 11, wherein the control system is configured to guideinert gas towards the reaction chamber via thermal atomic layerdeposition in-feed line(s) during the plasma atomic layer depositionperiod, the thermal atomic layer deposition in-feed line(s) beingseparate from plasma source line(s) via which radicals are guided intothe reaction chamber during the plasma atomic layer deposition period.19. The apparatus of claim 11, wherein said in-feed part is deformable,and the apparatus comprises at least one mechanical actuator to deformthe in-feed part between a contracted shape and an extended shape. 20.The apparatus of claim 19, wherein a substrate holder carrying at leastone substrate is mechanically coupled to the deformable in-feed part,and wherein deforming said deformable in-feed part causes said substrateholder carrying at least one substrate to lift into an upper positionfor loading or unloading.